1. Field of the Invention
The present invention relates to a dimmer switch for controlling the delivery of electrical voltage from a source to load which is especially useful in dimming lamps. More specifically, the invention relates to a dimmer switch having a broader range of control with a relatively simple circuit having a number of safety features.
2. Prior Art
Modern control circuits for dimmer switches commonly use a thyristor, most commonly a triac, to chop the AC power wave from an AC voltage source to the load, such as an incandescent light. A gate controls current flow through the triac, which is signaled to conduct by current flow through the gate. The switch that provides current varies depending on design; examples of devices that conduct current to the gate include an integrated circuit (IC) and another thyristor. However a lower cost dimmer switch may be provided by using a thyristor instead of an IC.
However, inductive loads are a concern when using a thyristor to control switching the power wave of from an AC power source. With inductive loads, dV/dt may become too large, and the sudden rise in voltage can cause the device to be triggered when not desired. Some have solved the problem by introducing “soft start” circuits into the dimming network. However, these circuits add cost and complexity to the switch.
Another concern in using a thyristor is that excessive current can cause damage to the thyristor when the thyristor fires and the potentiometer of a phase shift network, which governs the firing angle of the switch, is set too low. This problem is commonly solved by adding a protective resistor in series with the potentiometer. However, the addition of this additional resistor affects the firing angle of the phase shift network.
Thus, it is desirable to provide a simplified dimmer switch having a broad range of control while having desirable safety features.